1. Field of the Invention
The present invention relates to a method of, and apparatus for, charging/recharging secondary cells using transmitted microwave energy.
2. Description of the Related Art
The concept of generating dc power from transmitted radio waves is known from IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-32, No. Sep. 9, 1984 pages 1230 to 1242 "The History of Power Transmission by Radio Waves" by William C. Brown. The article reports that recovering dc power using a half-wave rectifier is an effective, relatively expensive and simple alternative compared to using a full wave rectifier. The rectifiers may be gallium arsenide Schottky--barrier diodes otherwise known as IMPATT devices.
U.S. Pat. No. 5,122,809 discloses a device for generating dc power directly from microwave energy. The device comprises a microstrip resonator having a line length of half a wavelength at the desired frequency. The resonator is split at its centre into 2 separate, aligned portions. A Schottky rectifier interconnects the adjacent ends of the separate portions of the resonator. No practical application is disclosed for the dc power generated.
Charging and/or recharging secondary cells normally requires connecting the cell(s) to a dedicated battery charger which a user does not carry with them. Additionally fast charging of cells normally takes at least 30 to 60 minutes which is not convenient in situations such as patrolling policemen where there is a requirement to be capable of maintaining radio contact whilst out on patrol. Accordingly there is a need to be able to recharge secondary cells very rapidly without requiring a dedicated battery charger.